G1301-f Picarro Instrument for Airborne Measurement of CO2 and CH4

See the figures below. Cavity ring-down is a technique where an oscillation in a cavity is damped by absorption, and the rate of damping is used to determine the concentration of the absorbing species. The diagrams includes the optical configuration, the typical detector response, and a typical "plumbing" configuration. A cryotrap removes water vapor, a primary interfering species.